Question

我正在尝试从iPhoneX TrueDepth相机保存深度图像。使用AVCamPhotoFilter示例代码，我可以在手机屏幕上实时查看转换为灰度格式的深度。我无法弄清楚如何以原始（16位或更多）格式保存深度图像序列。

我有nose.main()这是depthData的一个实例。其成员之一是AVDepthData，它是depthDataMap的实例，图片格式类型为CVPixelBuffer。有没有办法将其保存到手机以进行离线操作？

Answer 1

“原始”深度/差异地图没有标准视频格式，这可能与AVCapture没有真正提供记录方式有关。

你有几个值得研究的选择：

将深度贴图转换为灰度贴图（您可以使用AVCamPhotoFilter示例代码中的代码执行此操作），然后将这些贴图传递到AVAssetWriter以生成灰度视频。根据您选择的视频格式和灰度转换方法，您为阅读视频而编写的其他软件可能能够从灰度帧中以足够的精度恢复深度/差异信息。
只要您拥有CVPixelBuffer，您就可以自己获取数据并随意使用它。使用CVPixelBufferLockBaseAddress（带readOnly标志）确保内容在您阅读时不会更改，然后将指针CVPixelBufferGetBaseAddress提供的数据复制到您想要的任何位置。（使用其他像素缓冲区函数来查看要复制的字节数，并在完成后解锁缓冲区。）

但请注意：如果您花费太多时间从缓冲区复制或以其他方式保留它们，它们将不会被释放，因为新的缓冲区从捕获系统进入，并且您的捕获会话将挂起。（总而言之，如果没有测试设备是否具有内存和I / O带宽以便以这种方式进行大量录制，则不清楚。）

Answer 2

您可以使用Compression库创建包含原始CVPixelBuffer数据的zip文件。这个解决方案几乎没有问题。

这是很多数据和zip并不是一个很好的压缩。（压缩文件比每帧视频32位大20倍，帧数相同）。
Apple的Compression库会创建一个标准zip程序无法打开的文件。我在C代码中使用zlib来读取它并使用inflateInit2(&strm, -15);使其工作。
您需要做一些工作才能将文件导出应用程序

这是我的代码（我将其限制在250帧，因为它将其保存在RAM中，但如果需要更多帧，您可以刷新到磁盘）：

//  DepthCapture.swift
//  AVCamPhotoFilter
//
//  Created by Eyal Fink on 07/04/2018.
//  Copyright © 2018 Resonai. All rights reserved.
//
// Capture the depth pixelBuffer into a compress file.
// This is very hacky and there are lots of TODOs but instead we need to replace
// it with a much better compression (video compression)....

import AVFoundation
import Foundation
import Compression


class DepthCapture {
    let kErrorDomain = "DepthCapture"
    let maxNumberOfFrame = 250
    lazy var bufferSize = 640 * 480 * 2 * maxNumberOfFrame  // maxNumberOfFrame frames
    var dstBuffer: UnsafeMutablePointer<UInt8>?
    var frameCount: Int64 = 0
    var outputURL: URL?
    var compresserPtr: UnsafeMutablePointer<compression_stream>?
    var file: FileHandle?

    // All operations handling the compresser oobjects are done on the
    // porcessingQ so they will happen sequentially
    var processingQ = DispatchQueue(label: "compression",
                                    qos: .userInteractive)


    func reset() {
        frameCount = 0
        outputURL = nil
        if self.compresserPtr != nil {
            //free(compresserPtr!.pointee.dst_ptr)
            compression_stream_destroy(self.compresserPtr!)
            self.compresserPtr = nil
        }
        if self.file != nil {
            self.file!.closeFile()
            self.file = nil
        }
    }
    func prepareForRecording() {
        reset()
        // Create the output zip file, remove old one if exists
        let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] as NSString
        self.outputURL = URL(fileURLWithPath: documentsPath.appendingPathComponent("Depth"))
        FileManager.default.createFile(atPath: self.outputURL!.path, contents: nil, attributes: nil)
        self.file = FileHandle(forUpdatingAtPath: self.outputURL!.path)
        if self.file == nil {
            NSLog("Cannot create file at: \(self.outputURL!.path)")
            return
        }

        // Init the compression object
        compresserPtr = UnsafeMutablePointer<compression_stream>.allocate(capacity: 1)
        compression_stream_init(compresserPtr!, COMPRESSION_STREAM_ENCODE, COMPRESSION_ZLIB)
        dstBuffer = UnsafeMutablePointer<UInt8>.allocate(capacity: bufferSize)
        compresserPtr!.pointee.dst_ptr = dstBuffer!
        //defer { free(bufferPtr) }
        compresserPtr!.pointee.dst_size = bufferSize


    }
    func flush() {
        //let data = Data(bytesNoCopy: compresserPtr!.pointee.dst_ptr, count: bufferSize, deallocator: .none)
        let nBytes = bufferSize - compresserPtr!.pointee.dst_size
        print("Writing \(nBytes)")
        let data = Data(bytesNoCopy: dstBuffer!, count: nBytes, deallocator: .none)
        self.file?.write(data)
    }

    func startRecording() throws {
        processingQ.async {
            self.prepareForRecording()
        }
    }
    func addPixelBuffers(pixelBuffer: CVPixelBuffer) {
        processingQ.async {
            if self.frameCount >= self.maxNumberOfFrame {
                // TODO now!! flush when needed!!!
                print("MAXED OUT")
                return
            }

            CVPixelBufferLockBaseAddress(pixelBuffer, .readOnly)
            let add : UnsafeMutableRawPointer = CVPixelBufferGetBaseAddress(pixelBuffer)!
            self.compresserPtr!.pointee.src_ptr = UnsafePointer<UInt8>(add.assumingMemoryBound(to: UInt8.self))
            let height = CVPixelBufferGetHeight(pixelBuffer)
            self.compresserPtr!.pointee.src_size = CVPixelBufferGetBytesPerRow(pixelBuffer) * height
            let flags = Int32(0)
            let compression_status = compression_stream_process(self.compresserPtr!, flags)
            if compression_status != COMPRESSION_STATUS_OK {
                NSLog("Buffer compression retured: \(compression_status)")
                return
            }
            if self.compresserPtr!.pointee.src_size != 0 {
                NSLog("Compression lib didn't eat all data: \(compression_status)")
                return
            }
            CVPixelBufferUnlockBaseAddress(pixelBuffer, .readOnly)
            // TODO(eyal): flush when needed!!!
            self.frameCount += 1
            print("handled \(self.frameCount) buffers")
        }
    }
    func finishRecording(success: @escaping ((URL) -> Void)) throws {
        processingQ.async {
            let flags = Int32(COMPRESSION_STREAM_FINALIZE.rawValue)
            self.compresserPtr!.pointee.src_size = 0
            //compresserPtr!.pointee.src_ptr = UnsafePointer<UInt8>(0)
            let compression_status = compression_stream_process(self.compresserPtr!, flags)
            if compression_status != COMPRESSION_STATUS_END {
                NSLog("ERROR: Finish failed. compression retured: \(compression_status)")
                return
            }
            self.flush()
            DispatchQueue.main.sync {
                success(self.outputURL!)
            }
            self.reset()
        }
    }
}

保存TrueDepth相机的深度图像

2 个答案: